Digital content, such as an electronic book and an HTML document, is now widely used. However, in order to read those kinds of digital content documents, the reader may need to have a certain level of knowledge about the reading and meaning of a word including kanji (Chinese characters), for example. To make such a document easier to read even by a person who lacks the necessary level of knowledge, supplemental information, such as characters (ruby characters) showing the reading of a kanji, is displayed in the sentence.
In Patent Literature 1, there is disclosed a technology for generating text marked with ruby characters based on a user's rank and a difficulty level of a character string for which furigana (ruby characters) are to be provided.